Eranshahr and Eran were in use in
Iran. From early Sassanid era (
Shapour's elaborations), as a designation of their land they adopted Eranshahr “Empire of the
Iranians” and this served as the official name of their country.
Shahrestanhay-e-Eranshahr (lit. the provincial capitals of Iran) is a surviving Middle
Persian text on geography, which was completed in the late eighth or early ninth centuries AD. The text gives a numbered list of the cities of Eranshahr and their history and importance for Persian history. The text itself has indication that it was also redacted at the time of
Khosrau II in 7th century as it mentions several places in
Persian Gulf conquered by the Sassanid.
The book serves as a source for works on Middle Iranian languages, a source on Sassanid administrative geography and history, as well as a source of historical records concerning names of the Sassanid kings as the builder of the various cities. The text provides information on the Persian epic, the Khodaynameh (lit. Book of Kings)
The book may be the same as Ayadgar-e-Shahrha (lit. Memoir of Cities) named in the Bundahishn and said to have been written following an order of
Ardeshir I (reign until 241) the first king of the Sassanid Empire had used the older word Eran (
Parthian aryan) as part of his titles and in accordance with its etymology. At
Naghsh Rostam in
Fars province and the issued coins of the same period, Ardeshir I calls himself
Shahanshah-e-Eran in the Middle Persian version meaning “king of kings of the Aryans.” His son Shapour I referred to himself as Shahanshah-e-Eran and aneran (lit. "King of kings of the Aryans and the Non-Aryans") in Middle Persian. Later kings used the same or similar phrases and these titles became the standard designations of the Sassanid sovereigns.
However the major trilingual (Middle Persian, Parthian, and
Greek) inscription of Shapour I at the
Zoroaster's Cube in Fars, introduces another term Eranshahr in Middle Persian and Aryanshahr in Parthian. Shapour's declaration reads I am lord of the kingdom of the Aryans. This follows his title “king of kings of the Aryans,” and thus makes it "very likely" that Eranshahr "properly denoted the empire". Next to
Dariush's inscription, this inscription of Shapour at walls of Kabe-ye Zartosht is among the most important inscriptional records. It records parts of Persian-
Roman wars and gives "a clear picture of the extent of his empire" by naming of provinces, mentioning religious foundations and mentioning senior officials of the court of Papak, Ardeshir and Shapour I. According to the inscription, after death of Shapour's father and his accession, the emperor Gordianus “marched on
Assyria, against Eranshahr and against us”.
Beside the royal title, the term "Eran" was also used as an abbreviation of "Eranshahr" and referred to the empire in the early Sassanid era. In this case the Roman west was correspondingly referred to as “aneran”. As references to empires, Eran and Aneran occur already in a chronicle text from
Mani (dating back probably to Ardeshir I's era.) This shorter term "Eran" appears in the names of the towns build by Shapour I and his successors as well as in the titles of several high ranking administrative officials and military commanders.
According to the book and as an ancient Iranian tradition, Eranshahr is divided into four mythological regions or sides called kust. These parts/regions/sides of the state during and after
Khosrau I, on the pattern of the four cardinal points, are
Khorasan “northeast”; Khavarvaran “southwest”; Nemroz “southeast”; and Adurbadagan “northwest”.
The kusts were named diagonally beginning from northeast to southwest and from southeast to northwest-a style likely following an Old Persian tradition in naming satraps. The usual Middle Persian term "abakhtar" used for northern direction in ancient Iranian tradition has been avoided in this designation and replaced by the name of their province Adurbadagan. This is believed to be because of "the
Zoroastrian association of the north with the abode of evil" which "would be evoked by use of abakhtar".